Uwatec D420 User manual
D420 Service Manual
Use this manual at your own risk. It is not approved by Scubapro.
DIY service of scuba life support equipment may kill you.
This manual has been adapted from a copy of Version 1.0, March 2020
D420 SERVICE PROCEDURE, D420 SECOND STAGE GUIDELINES,
DISASSEMBLY, ASSEMBLY, ADJUSTING AND FINAL TEST,
published by Johnson Outdoors. As no copyright notice was observed on the
document, any use of copyrighted material is unintended and inadvertent.
The document had apparently been translated from the Italian, and text has
been modified for clarity where translated phrases were unclear.
The author has made additions and modifications based upon his experience,
which have not been approved by Scubapro.
Use this document at your own risk.
2
Contents
General Notes ............................................................................................................................. 2
Cleaning Procedures ................................................................................................................... 2
Seals and o-rings ........................................................................................................................ 2
Plastic or rubber components ...................................................................................................... 2
Metallic Components ................................................................................................................... 2
Tools ............................................................................................................................................ 3
Disassembly Procedure ................................................................................................................ 4
Reassembly Procedure ................................................................................................................. 6
Tuning and Final Testing ............................................................................................................. 9
General Notes
This regulator is designed for use with Enriched Gas (Nitrox) to EAN40. Use only perfectly
cleaned tools in a cleaned environment
Cleaning procedure
Please refer to the "SCUBAPRO CLEANING PROCEDURE" document
Seals and O-Rings
• All seals and o-rings shall be perfectly clean.
• Check o-ring lands for imperfections or burrs, and clean as needed.
• All o-rings, in particular those for dynamic use, must be lubricated, along with any adjacent
moving parts. The approved lubricant is Christolube MCG-111. Previous Technician
Seminars have indicated that Tribolube 71 is also acceptable, though this is not found in
official Scubapro publications.
• Note: The lubricant container, as well as tools and brushes used for service must be
perfectly clean, free from dust, hydrocarbons or other particulate matter.
Plastic or rubber components
• The components, particularly on sealing surfaces, should be free of deformation or damage.
• All threaded components should screw freely and without resistance, leaving no excessive
gap, unless otherwise specified.
Metallic components
• Metallic components should not have separated from the regulator or regulator part.
Chrome plating should be smooth without deformation, imperfections or damage.
3
Tools
• Flat blade screwdrivers, 2.5mm and 5mm
• Non-serrated thin bladed, sharp knife
• Pin punch (MK2 seat tool) PN 43.300.210
or 1.5mm hex key
• Flow Vane Face Spanner PN 43.420.012 or small pin face spanner
• Scubapro Multitool PN 43.040.000 or small pin face spanner
• 3/32" Allen key PN 43.002.101
• 2mm, 5mm and 6mm hex keys
• O-ring pick PN 43.300.107
• 3/16” wooden dowel or blunt brass pick
• Small needle nose pliers, forceps or tweezers
• Front Ring Retaining Tool PN 43.404.003
or rubberized “jar lid remover”
• Torque wrench PN 43.300.998
• 6mm Hex drive extension PN 43.040.009
4
Disassembly Procedure
1. Remove the mouthpiece clip or zip tie and the mouthpiece.
2. Lift the cover pin (48) from the case by using an
appropriate tool (e.g. 2.5 mm screwdriver), and then grasp
carefully with forceps and remove.
3. Using a thin-bladed knife, carefully lift the decal (36) from
the flow vane cap (35). Avoid scratching the flow vane
plug (35) beneath the decal.
4. Push the purge lever pin (45) out of the case with a pin
punch (MK2 HP seat tool) or 1.5mm hex key. Remove the
purge button (44) and spring (43) and set aside.
5. Unscrew the face plate (42), rotating counterclockwise
from the case. If necessary, use the SCUBAPRO D420
special tool PN 43.404.003 or a rubberized pad.
6. Carefully lift out the diaphragm thrust washer (41) and the
diaphragm (40).
7. By using the multi tool (function #9) or a face spanner
with a counterclockwise motion, unscrew the flow vane
plug (35) from the case.
8. The dive switch (33) and the flow vane washer (32) can
then be lifted out. O-ring (34) may fall out at this time.
9. Use a 3/32" Allen key to fully unscrew the small lever hex
screw (16) from the bottom of the housing (18). The lever
(37) will now be loose and it can be carefully removed.
10. Remove the decorative cap (11) from the case plug (10)
by carefully lifting with a brass spade or a flat blade
screwdriver.
11. Using a 6mm Allen key, unscrew the case plug. Use a
brass pick to carefully remove both o-rings.
12. Next, unscrew the hose inlet (5) with a 6mm Allen key and
pull it out from the housing support (8). As above,
carefully remove both o-rings (6).
5
13. By using a face spanner or tool PN 43.420.012 grasp the
tabs on the flow vane ring (31) and unscrew it from the
case by rotating counter clockwise. The sub-assembly
consisting of the flow vane ring (31), two o-rings (28
and 30), the flow vane (29), the hex adjuster screw (27)
and possibly o-ring (34) is now loose.
Note: the spring (25) and the spring support (26) are
also now loose. Use care to avoid dropping parts with
the next step.
Holding the case upright, lift the assembly from the
case. Then carefully turning the case upside down,
collect the spring (25) and spring support (26) in your
hand as they fall out. The poppet (stem assembly) (49)
may also fall out.
14. Then, grasping the flow vane ring (31), pull it apart
from the flow vane (29). Remove o-ring (30) and
o-ring (28). Using a 5mm Allen key, engage the
adjustment screw (27), loosen it clockwise and remove
from the flow vane from below. Its o-ring (34), if it has
not fallen out before, will now be loose. Remove it.
15. Pushing in an upward direction against the square
deflector at the rear of the housing (18), push the
housing up and out of the case.
If it did not fall out in step 13. above, the poppet
(stem assy) (49) is accessible and can be carefully
removed with a thumb and index finger or small
forceps.
16. Push the housing support (8) in the direction of the LP
hose inlet (i.e., from the opposite side). Push it out of
the case and remove the o-rings (7) with a brass or
plastic pick, being careful not to score the o-ring
groove.
17. Use a pin punch or 2mm hex key to remove the exhaust
tee pin (12). The exhaust tee (14) is now removable
from the case.
Note: the exhaust tee is thinner and more delicate than
the case. To avoid breakage, use care in sliding the ears
of the tee around and off the case.
18. The exhaust valve (13) is now accessible and can be
replaced, if necessary. Inspect the valve for complete
sealing against the case. Inspect the edge for damage.
Confirm that the barb is locked inside the spokes on the
case. The exhaust valve is not normally removed at
annual service, unless damaged.
DISASSEMBLY IS NOW COMPLETE
6
Reassembly Procedure
1. If the exhaust valve (13) must be replaced, first ensure the land
where the valve edge will seal is clean and without scratches.
Remove the old valve by cutting the barb of the center silicone
nipple where it penetrates the inside of the case. Insert the new
valve by carefully pulling on the center nipple from the inside
of the case, and ensure that the barb has completely entered the
case. Check valve retention by slightly pulling the leaflet
outwards. Cut the nipple off short, leaving approx. 1mm
beyond the end of the barb.
2. Carefully fit the exhaust tee (14) around the case, without
excessively bending the ears of the tee. Insert the pin (12) in
the case, verifying that the pin enters with some friction.
Ensure that the pin rests equally on both ends. Check that the
exhaust valve is not pinched between the case and the tee.
Many Scubapro o-rings are numbered via an eight
digit system that typically follows the format
01.050.xxx. In this manual, o-rings will hereinafter be
described only with the last three digits following a
decimal point (e.g. .160), as well as with the diagram
number in parentheses. The full part number will be
listed where it does not follow the 01.050. format.
3. Lightly lubricate two .160 o-rings (7) and carefully fit them into
the grooves of the housing support (8). Assure that they are not
twisted. Next, lubricate four .364 o-rings (6). Fit two onto the
hose inlet (5), and two onto the case plug (10).
4. Holding the second stage with the mouthpiece tube facing
towards you, insert the housing support (8) inside the case (15)
from the right side. Make sure the notch in the housing support
is facing upwards and away from you.
5. Carefully remove the housing (18) from its paper wrapper.
Note especially that the circular knife edge in the top of the
housing is delicate, and must not be allowed to contact tools or
any metal instrument. Inspect this knife edge for damage or
defects. It should be flat and even. If any imperfections are
noted, do not use the housing, and obtain a replacement from
another service kit.
7
5. Hold the housing with the square flap facing
downward and toward you, and the case with the
mouthpiece tube facing toward you. Insert the
housing into the support, and using only the ball of
your thumb, press it downward fully, engaging the
tooth on the housing in the notch of the housing
support. Take special care to not put any pressure on
the knife edge. Inspect the housing placement by
looking through both sides of the housing support
(where the hose inlet and plug will be inserted), and
ensure that the housing’s side holes are centered in
the support.
7. Using a 6mm Allen key, screw the hose inlet (5) and
the plug (10) into the housing support. Note that the
hose can be mounted on either side of the regulator.
Standard hose position is to have the hose inlet (5) on
your right, when the case is held with the mouthpiece
tube toward you.
8. Using a 6mm hex extension attached to a torque
wrench, tighten the hose inlet in the case to 44 in-lb
(5 Nm). With a 6mm hex key, tighten the case plug
finger tight.
9. Place the case flat on the bench in front of you,
mouthpiece tube facing down. Insert the lever (37)
from the left side into the oval hole in the housing
such that the narrowed flat in the lever is centered.
Gently allow the lever to drop against the square flap
of the housing.
10. Insert the hex screw (16) unthreaded end first, and
using a 3/32"Allen key, screw the hex in until it is just
flush with the bottom of the housing. Set the regulator
aside briefly.
11. Lightly lubricate the .177 (28) and .164 (30) o-rings.
Carefully place the .164 o-ring (28) in the dedicated
groove of the flow vane (29) and the .177 o-ring (30)
in the groove of the flow vane ring (31). Ensure
that they are not twisted.
12. Using a 5mm hex key screwing counterclockwise
from above, and pushing up from below, insert and
screw the adjustment screw (27) all the way into the
flow vane (29) until it stops. Do not force the screw
past the stop.
In this picture, the lever has been
raised to facilitate viewing the initial
position of the hex screw. The lever
will normally fall against the square
flap of the housing once the hex has
been screwed into position, until the
poppet and spring have been added.
8
13. Press fit the flow vane (29) inside the flow vane ring (31), until the
vane is up against the ring and the teeth of the two parts are at the
same level. Set this assembly aside.
14. Remove the poppet (stem assy) (49) from its paper envelope.
Handling it carefully, generously lubricate the .323 o-ring at the
base of the poppet (stem assembly) (49).
15. Returning to the regulator set aside earlier, and using a pair of
tweezers, forceps or other delicate instrument, grasp the poppet
(stem assembly) (49) by the top nut and carefully insert it in the
opening made by the housing knife edge. Take care to not strike
the knife edge with the metal end of the poppet. Lower the poppet
into position, until its round top is contained within the four teeth
of the housing, and the nut is uppermost.
16. Set the spring support (26) on the top of the spring (25), and
carefully balance both on top of the poppet in the regulator
housing. Taking the flow vane sub-assembly from step 13. above,
screw the whole unit all the way in into the case (15), first by
hand, and then using a special tool (PN 43.420.012) or a pin
spanner braced against the two teeth of the flow vane ring. Do
not force it, but tighten it, stopping with teeth at 12 & 6 o’clock.
17. NOTE: It is critical that the teeth of the flow vane ring (31) and
the flow vane (29) are positioned in a 12 o’clock/6 o’clock
orientation. Rotate the inner flow vane until its biggest tooth rests
at the 12 o’clock position with the mouthpiece up.
18. Insert the flow vane washer (32), ensuring that when the tab is in
the slot of the case, the grooves meet the teeth of the flow vane
ring (31). Rotate the flow vane ring slightly as needed to allow the
washer to fall into place. Insert the dive switch (33), matching its
larger groove to the bigger tooth in the flow vane (29). Insert a
lightly lubricated .347 o-ring (34) into the space around the hex
adjustment screw (27). Insert the flow vane plug (35), and using a
pin spanner or the Multitool (function #9), tighten it clockwise.
Do not tighten excessively. Move the dive switch to be sure it
slides freely with a minimum of friction.
19. Holding the regulator mouthpiece down, screw or unscrew the
lever adjustment hex screw (16) with a 3/32"Allen key, until the
top edge of the lever is level with the rim of the case. Note that if
the regulator is instead held vertically, the lever may fall
forward of the plane of the case rim, giving incorrect feedback
regarding lever height.
NOTE: To avoid unnecessary play in the lever, it is best to make the
adjustment above while the 2nd stage is pressurized, as the lever
will drop 0.25-0.5mm upon pressurization. See Tuning and Final
Adjustment below.
20. Examine the diaphragm (38) for cuts, holes or an irregular edge.
Check that the disc insert (50) is secure in its groove in the
diaphragm. Do not insert the diaphragm at this time.
9
Tuning and Final Testing
1. Connect the second stage to the LP hose and pressurize the regulator with 125-145 psi. Using a
5mm hex key, turn the adjustment screw (27) just until there is no air leak.
NOTE: Rotating the adjustment screw clockwise increases spring tension on the poppet, and
increases inhalation effort (“cracking effort”); counterclockwise rotation decreases spring load
and lowers cracking effort.
2. Insert the diaphragm assembly (40) in the groove of the case (15). Using a small dowel or other
blunt tool, confirm that the diaphragm rim is fully seated in the groove. Do NOT lubricate the
diaphragm edges.
3. NOTE: This next step specifically differs from a subsequent
instruction in the translated Scubapro manual.
Before attaching the faceplate, tap lightly with one finger on
the center disc of the diaphragm, and confirm that when the
regulator is pressurized, there is approximately 0.25-0.5mm of
separation between the lever and the diaphragm disc. That
separation may disappear when the regulator is depressurized.
Adjust lever height with a 3/32” hex key in the lever hex screw
(16).
4. Insert the thrust washer (ring) (41), again ensuring that it is fully seated, and then screw on the
faceplate (retaining ring) (42) using your palm or a suitable tool (PN 43.404.003), until the hole
in the faceplate is aligned with the same hole in the case (15). Note: the thrust washer (41)will
pull the sides of the diaphragm inward slightly as the faceplate is screwed in. Therefore, tap the
diaphragm disc to confirm that there is a tiny gap between the lever and the diaphragm center
disc (in contrast with Step 6 below). If a gap is not found, remove the diaphragm and adjust the
hex screw (16) counterclockwise to lower the lever fractionally.
5. Insert the purge button spring (43) into its groove in the case (15). Carefully fit the purge
button (44) into the case, ensuring that the restraining hook at the bottom of the purge button is
inside the cutout in the faceplate. Using pressure against the spring to align the holes in the top
of the purge button with the holes in the case, secure the purge button with the pin (45).
Confirm that the pin enters with some friction, and that it is symmetric on both ends. Operate
the purge button and confirm that it returns freely when pressed.
Deleted from the translated SP manual: 6. Be sure that the lever is in contact with the diaphragm
disc and the value of the cracking effort measured with the Magnehelic shall be in the range
between 1.2-1.6 Inch H20. If this is not the case, disassemble the components previously
assembled in the above points 2, [4] and [5] of this chapter, then adjust the hex screw (16) with a
3/32"Allen key, reassemble the components and re-adjust the screw adj, (27): rotating clockwise
will increase the inhalation effort. Repeat these operations until you reach the cracking effort
required while at the same the lever is in contact with the diaphragm disc.
It has been this author’s observation that if the lever is in contact with the diaphragm when
the regulator is pressurized, diaphragm elasticity may apply a counterforce to the poppet
spring whenever the spring adjuster is screwed in, making tuning unstable. By design, this
theoretically shouldn’t occur, due to the presence of a retaining hook at the bottom of the
purge lever which should prevent the diaphragm from being placed under tension by the valve
lever. Nonetheless, tuning instability has repeatedly been noted when Step 6 is followed as
written, and that same instability disappeared when the lever was lowered 0.25-0.5mm.
Note however, that lowering the lever decreases maximum valve opening. A significant
decrease in lever excursion could lead to inadequate air delivery and death. Therefore,
anyone following these steps must assess for her/himself whether a loss of 0.5mm in lever
excursion is significant. A substitute Step 6 is inserted below.
10
6 (Substitute). With the regulator pressurized and with a
0.25-0.5mm gap present between the back of the diaphragm disc
and the lever, turn the adjustment screw (27) to change cracking
effort.
NOTE AGAIN: Scubapro prescribes no gap between lever and
diaphragm in the original Service Manual.
Turning the adjustment screw (27) clockwise increases cracking
effort and counterclockwise decreases cracking effort. The cracking
effort should be set to 1.2-1.6 inches water column on the
magnehelic. Due to case geometry and the huge air delivery of this
center-balanced design, tuning this regulator “hot”
(below specification) is specifically not recommended.
For best practice, the adjustment screw should be turned
only when the purge lever is depressed, to avoid the
possibility that spring binding against the poppet will cause
the knife edge to cut the seat. Therefore, to minimize air
supply loss when the purge is pressed, a LP hose “On/Off”
slide valve can be used to quickly depressurize the regulator
during adjustments, in lieu of repeatedly turning off the gas
supply and depressurizing the hoses before pressing the
purge button.
7. Attach the mouthpiece (47) to the case with the clip (46) or zip tie.
8. Place the dive switch in the Pre-Dive position (forward), and
confirm that freeflow cannot be initiated with a brisk tap on the
purge valve. If freeflow occurs in the Pre-Dive position, confirm
that
a) the mouthpiece is in place,
b) the supplied Intermediate Pressure is 125-145 psi,
c) that cracking effort is at least 1.2”WC, and
d) that the flow vane subassembly has been correctly
assembled and installed.
7. Depressurize the system, and perform a leak test without air supply,
or by closing the inlet with a finger or a plug. Using light suction
applied to the mouthpiece, create a vacuum and assure that there is
no leak into the case. Any leak on suction may require examination
or disassembly to highlight a possible hole in the diaphragm or
exhaust valve, or a malpositioning of the exhaust valve sealing
edge. A cracked case may also be revealed by this test.
8. Apply the decal (36) to the flow vane cap (35), paying attention to
its orientation. Apply the decal centered in its groove and
positioned as shown in the picture(s) adjacent.
9. Fit the safety pin (48) into the aligned holes of the case (15) and
faceplate (42).
10. Press the decorative cap (11) into the hex recess of the case plug
(10), ensuring that it is secure, and there is no gap between the
plastic trim and the metal plug.
THIS COMPLETES REASSEMBLY AND TUNING
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